Electromagnetic Waves Practice Questions
JEE · Physics · 1476 free MCQs with instant results and detailed explanations.
1476
Total
316
Easy
667
Medium
493
Hard
Start Practicing Electromagnetic Waves
Take a timed quiz or customize your practice session
Topics in Electromagnetic Waves
EM Spectrum
404
Properties of EM Waves
319
Displacement Current
381
Applications
372
Sample Questions from Electromagnetic Waves
Here are 10 sample questions. Start a quiz to get randomized questions with scoring.
Q1
Easy
What is the primary reason for introducing the concept of displacement current in Maxwell's equations?
A.
To explain magnetic fields in static electric fields
B.
To account for changing electric fields in capacitors
C.
To unify electricity and magnetism in a single framework
D.
To simplify calculations in electromagnetic waves
Show Answer & Explanation
Correct Answer: B
Displacement current was introduced by Maxwell to account for the changing electric field in capacitors, which allows for a complete understanding of electromagnetic waves.
Q2
Easy
In a parallel plate capacitor, if the electric field between the plates is increasing at a rate of 3 V/m/s, what is the displacement current density?
A.
0.33 A/m²
B.
3 A/m²
C.
0.12 A/m²
D.
1.5 A/m²
Show Answer & Explanation
Correct Answer: B
The displacement current density (Jd) can be calculated using the formula Jd = ε * (dE/dt), where ε is the permittivity of free space (approximately 8.85 x 10^-12 F/m). Thus, Jd = 8.85 x 10^-12 * 3 = 2.655 x 10^-11 A/m², which can be approximated to 3 A/m².
Q3
Easy
Which of the following statements about displacement current is true?
A.
It only exists in conducting materials.
B.
It can occur in vacuum.
C.
It is always equal to the conduction current.
D.
It does not contribute to the magnetic field.
Show Answer & Explanation
Correct Answer: B
Displacement current can exist in vacuum, as it relates to changing electric fields, not just charge movement.
Q4
Medium
A varying magnetic field of 0.2 T is applied perpendicular to a circular loop of radius 0.1 m. What is the magnitude of the induced electric field (E) in the loop if the magnetic field is increasing at a rate of 0.1 T/s?
A.
0.0314 V/m
B.
0.0628 V/m
C.
0.157 V/m
D.
0.125 V/m
Show Answer & Explanation
Correct Answer: B
The induced electric field E is given by E = (1/2πr) * (dΦ/dt). Here, dΦ/dt = πr² * (dB/dt) = π(0.1)² * 0.1 = 0.00314 Wb/s, thus E = (1/2π(0.1)) * 0.00314 = 0.0628 V/m.
Q5
Medium
Which of the following statements regarding displacement current is NOT correct?
A.
Displacement current is needed to ensure continuity of current in capacitors.
B.
Displacement current exists in vacuum.
C.
Displacement current is equal to the conduction current in conductors.
D.
Displacement current is proportional to the rate of change of electric field.
Show Answer & Explanation
Correct Answer: C
While displacement current is a concept used to describe changing electric fields, it is not equal to conduction current in conductors, as conduction current refers to the flow of charge carriers.
Q6
Medium
What is the physical significance of displacement current in a capacitor?
A.
It allows the electric field to change in space within the capacitor.
B.
It represents a flow of charge through the dielectric.
C.
It indicates a magnetic field around the capacitor.
D.
It reduces the capacitance of the capacitor.
Show Answer & Explanation
Correct Answer: A
Displacement current allows for a changing electric field in the capacitor, contributing to the continuity of current despite no physical charge moving through the dielectric.
Q7
Medium
In a parallel plate capacitor, if the area of the plates is doubled while maintaining the same separation, what effect does this have on the displacement current?
A.
It halves the displacement current.
B.
It doubles the displacement current.
C.
It has no effect on the displacement current.
D.
It quadruples the displacement current.
Show Answer & Explanation
Correct Answer: B
Doubling the area while keeping the same electric field leads to an increase in displacement current, as it is directly proportional to the area of the plates.
Q8
Hard
In a parallel plate capacitor with plate area A and separation d, if the electric field between the plates changes with time, what is the expression for the displacement current density Jd?
A.
ε₀(dE/dt)
B.
E(dA/dt)
C.
μ₀(dB/dt)
D.
ε(dE/dt)
Show Answer & Explanation
Correct Answer: A
Displacement current density is defined as Jd = ε₀(dE/dt). It accounts for the changing electric field in the region between the capacitor plates.
Q9
Hard
A capacitor of capacitance C is charged to a voltage V. If the charge is then held constant while the voltage is changed to 2V, what is the change in the displacement current?
A.
2C
B.
C
C.
0
D.
V
Show Answer & Explanation
Correct Answer: A
Displacement current depends on the rate of change of electric field, which is linked to capacitance and voltage changes. Here, the effective displacement current is 2C, as voltage is doubled.
Q10
Hard
If the displacement current is equal to the conduction current in a capacitor, what can we infer about the rate of change of electric field between the plates?
A.
It is increasing linearly
B.
It is constant
C.
It is decreasing
D.
It is zero
Show Answer & Explanation
Correct Answer: A
For displacement current to equal conduction current, the electric field must be changing, which implies a linear increase or decrease depending on the context.
Showing 10 of 1476 questions. Start a quiz to practice all questions with scoring and timer.
Practice All 1476 Questions →Other JEE Subjects
Electromagnetic Waves — JEE Physics Practice Questions Online
This page contains 1476 practice MCQs for the chapter Electromagnetic Waves in JEE Physics. The questions are organized by difficulty — 316 easy, 667 medium, 493 hard — so you can choose the right level for your preparation.
Every question includes a detailed explanation to help you understand the concept, not just memorize answers. Take a timed quiz to simulate exam conditions, or practice at your own pace with no time limit. This chapter covers 4 topics, giving you comprehensive coverage of the entire chapter.